1. Field of the Invention
The present invention relates to an optical detector, and more particularly, to an optical detector having external light cut-off units in order to increase a recognition rate for test signals incident to optical sensors used in an auto convergence of a projection television (TV).
2. Description of the Related Art
An image display apparatus starts from a small model such as a 14-inch analog TV and has developed up to a projection TV of more than 60-inch currently.
The projection TV is an apparatus so configured as to project red(R), green (G), blue (B) colors onto a screen using an each projection cathode-ray tube (PRT) to display images on a screen. Sensitivity quality of the projection TV includes: a white uniformity (W/U), a bright uniformity (B/U), convergence, focus, and distortion.
Here, the convergence denotes a phenomenon that R, G, B beams discharged from the PRT are gathered at one single point on a screen by a magnetic field of a deflection yoke. If the beams are not deflected as desired due to a malfunction of the deflection yoke or an influence of the magnetic field, a mis-convergence is generated and a color-biased phenomenon is generated on a screen as illustrated in FIG. 1.
Therefore, in FIG. 1, a projected picture should be properly corrected into a corrected picture as illustrated through a horizontal convergence correction and a vertical convergence correction.
For example, three beams R, G, and B should be exactly gathered onto one single point to be shown as white. If a mis-convergence is generated, a line taking on abnormal other colors such as R, G, and B colors is shown to a side of a white line, which acts as a factor that deteriorates a quality of a screen.
Therefore, a technology in which a user can directly correct a convergence is required.
Recently, for the technology in which a user corrects a convergence, there exist an EZ focus in which a user manually corrects a central portion, an upper portion, a lower portion, a left portion, a right portion, and corner portions of an image displayed on a screen, and an auto-convergence system in which detectors are arranged on a backside of a front cabinet for supporting a screen of a projection TV to detect a degree in which a convergence is distorted and thus automatically correct the convergence.
Here, the auto-convergence system basically generates a predetermined pattern on a screen and recognizes a distortion degree of the convergence using optical sensors and then corrects the distortion.
Recently, with a high-quality trend of a projection TV, the auto-convergence function of the projection TV is commercialized.
A related art projection TV will be described below with reference to the accompanying drawings.
FIG. 1 is a view illustrating a screen in which mis-convergence is generated, FIGS. 2A and 2B are a front view and a sided view illustrating that optical sensors are mounted respectively on a general projection TV, and FIG. 3 is a flowchart illustrating a method for performing an auto-convergence of a projection TV according to the related art.
To perform an auto-convergence function in the projection TV, a first to an eighth optical sensors 11 to 18 are mounted on four corners of up/down/left/right and upper middle/lower middle/left middle/right middle portions around a screen as illustrated in FIG. 2.
Test signals projected from the PRTs 21, 22, and 23 are incident to the first to eighth optical sensors 11 to 18 by way of a reflector 20, so that the auto-convergence is performed using the test signals detected by the first to the eighth optical sensors 11 to 18.
However, since the optical sensors are exposed to an inside of a path of external light in the first to the eighth optical sensors 11 to 18 mounted as described above, there might occur a case that the optical sensors cannot recognize the test signals due to the external light if brightness of the outside of an image display apparatus is bright.
A related art method for controlling an auto-convergence will be described with reference to FIG. 3. First, if an auto-convergence is performed, whether there exists a signal input is judged (S10 and S11).
After that, if the signal input exists as a result of the judgment (S11), whether external light is detected is judged (S12).
If the external light is detected as a result of the judgment (S12), the screen is restored to a factory-set state and an on-screen display (OSD) which says “control again after making ambient light dark” is displayed (S13 and S14).
If a user inputs a power-off command, a system is ended. Otherwise, the initial step S11 is performed (S15).
In the meantime, if the external light is not detected as a result of the judgment (S12), a first auto-convergence is performed (S16).
Subsequently, whether a signal exists is judged (S17).
If the signal exists as a result of the judgment (S17), whether an error is found in a sensor value detected by the first to the eighth optical sensors is judged (S18).
After that, if the error is found in the sensor value as a result of the judgment (S18), a factory-set state is restored and a second auto-convergence is performed (S19 and S20).
Further, whether a signal exists is judged (S21).
If the signal exists, whether an error is found in a sensor value detected by the first to the eighth optical sensors is judged (S22).
After that, if the error is not found in a sensor value as a result of the judgment (S22), an auto-convergence correction is performed (S23).
In the meantime, if a signal does not exist or the error is found in the sensor value as a result of the judgments S17, S21, and S22, a factory-set state is restored and the step S15 is performed (S24).
If a signal input does not exist initially as a result of the judgment (S11), an OSD that says “control again after a signal is inputted” is displayed (S25).
According to a related art image display apparatus, optical sensors are exposed to an inside of a path of the external light, so there might occur a case that the optical sensors cannot recognize a test signal due to the external light when a place where a TV is installed is bright. In that case, there is an inconvenience that the auto-convergence should be performed again after making surroundings sufficiently dark.